Blown Slave Cylinder

Canuk40 said:

Hi Mitchell,

Compare the slave cylinder length in your picture to the length measured from the mounting hole to where the slaves' pushrod would contact the clutch fork inside the transaxle.

The distance measured inside the transaxle should shorter than the bare cylinder by almost the length of the stroke of the pushrod. If that works out ok then either the fork is jammed or the two new slave cylinders are both bad, or something else is going on (throw out bearing stuck?).

If you wanted to check the slave cylinder outside the car to see exactly where its' leaking you would have to compress the pushrod in almost the full stroke, then try bleeding the part. It wont be easy to clamp or retain the pushrod in the retracted position but nothing will be learned by testing it without the pushrod retracted.

The chances of buying two bad slave cylinders is pretty low, however having three cylinders acting the same way would point to something other than the slave cylinders in my mind.

If the fork distance to the mounting hole dimension is the same or greater as your slave cylinder at rest the it's definitely the fork.

It's a great mystery at this point...

Cheers
Ian

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Canuk40 said:

Hi Mitchell
Sounds like a plan, you will know how much the slave pushrod moved back into it's housing. That length is your available stroke to lift the clutch. Can't wait to hear what you find out.

Cheers
Ian

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Canuk40 said:

I should add that some clutch master cylinders can be very difficult to bleed by the standard pump the pedal method. Mitchell have you tried vacuum bleeding the clutch circuit? Cheers

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blueovalz said:

Still trying to understand why hitting the stops, or misalignment causes a leak. Brakes basically hit a solid stop hydraulically, yet the MCs don't leak because of that. Randy's post #7 seems to be "it", unless the design is faulty (which could be being this is the second of two (same design or product) that has leaked.

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Canuk40 said:

Hi Mitchell,

If there's no visible damage to the seal or piston bore then the slave cylinder should work. If you have three cylinders acting the same way it's hard to point at the slave cylinder being the culprit.

That doesn't explain why or how clutch fluid was getting past the seal and into the dust boot. Does the clutch slave leak fluid past the seal and dust boot when pressurized to normal clutch actuation levels while not mounted in the transaxle?

I have not tried this as such, but once I noticed it was buggered I pulled it out of the car and it would build up a lot more pressure to the point the pedal could not be compressed until bleed opened. (Although a small amount of fluid did leak out still)

That would test a leak scenario simulating the slave piston is not engaging the clutch fork arm when installed.

If you can generate enough pressure in the system to blow past the seal then there could not be air in the system. How hard to pump was the clutch pedal when there were fluid leaks seen in the dust boot?

my wife was doing the pedal work but when leakin the clutch would just keep going to the floor and reservoir would drop.

Was that more or less pedal pressure than you remember when the clutch was working before the slave cylinder swap?

id say more pressure when working

When bleeding the system how much did the fluid level drop in the clutch reservoir? Did the fluid level in the reservoir ever drop out of sight? If it did then air could have been introduced into the clutch circuit.

fluid was in the reservoir the whole timel

There is no adjustment in the clutch slave to the transaxle case to the clutch fork to the throwout bearing to the clutch pressure plate fingers. If all those parts are good parts and not operating properly it's an assembly issue or air in the line. It's a head scratcher to analyze remotely for sure...

Cheers
Ian

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blueovalz said:

Ian is on the mark here, but the exact positioning of seal is critical in that when you "just see the bottom...". If you can see the pressure flap (the directional, concave portion of the seal or Rubber Cup in the above diagram (the edge of the lip that is facing rearward), it would seem that fluid pressure at that point cannot swell the lip radially outward to seal the cylinder because pressure is applied now to the wrong side of this flap or lip. If the lip (flap) is not visible, and you only can see the base of the seal (NOT the edge of the lip), then you may have a properly positioned piston/seal. Looking at the photo (out of focus, or I need new glasses), it looks too close to call, because it appears you are looking at the base of the seal, but surely the lip is extremely close to the port at that position based on the other photo of the piston only.

If indeed the seal is too far rearward, a shim or some means of forcing the piston just a mm or two, forward should help (the small protrusion at the rear of the piston in the drawing above would be too short). If indeed the seal is too far rearward, that to me indicates a faulty design or machining, and perhaps why you've had two in a row with this problem. If the lip is not positioned, it would allow some amount of fluid (not much) by the seal until the piston moved forward and properly stopped any leakage. Heck, stick a penny in the end of the bore, reassemble, and go with it .


I left the lip (cup if you will) in the drawing below "relaxed" so that it better illustrated my point. Normally it would be compressed in the bore.

View attachment 118965

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IanAnderson said:

My gut would say that no you should not be able to see the seal when you look down the bleed or fill hole. In my head that would mean that the fluid would have a way past the seal in your picture a little dogleg upwards near the bleed nipple past th e seal and into the dust gator.

Does it have a "rubber cup" missing as seen in this image that will stop the piston so that the seal never moves further than thebore and not into the bleed nipple area?


View attachment 118964

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Canuk40 said:

Hi Mitch,

I'd really like this not turn into an engine out although you should be able to sneak the transaxle out on it's own.

Probabilities are 1) air in system 2) something wrong between the slave and clutch pressure plate fingers 3) defective clutch slave cylinder.

If each slave was bench tested by holding it in a vise at the fully retracted length it would be east to bleed, pressurize and measure the psi the part can handle without leaking. Then you'll know which or none of the slaves are ok.

If they are ok, we're back to air in the system or a problem with the other clutch actuation parts.

Cheers
Ian

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347Stroker said:

Would I need to have the cylinder fully compressed or could I have it half compressed. That would at least prove the seal. Then to get it in o would have to release fluid but if it fails when it's then installed, it will mean the push rod is Too long. To be honest I may just shorten pushrod anyway.

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